What's torture is reading historical stuff taken out of context. Who was Asano, anyway? A little googling tells us

A U.S. Military Commission at Yokohama, Japan. tried four Japanese defendants for torture and mistreatment of American and Allied prisoners at Fukoka Prisoner of War Branch Camp Number 3, in Kyushu. Water torture was among the acts alleged in the specifications against the various defendants, and it loomed large in the evidence presented against them.[56]

The four defendants, Hata,[57]Asano,[58] Kita,[59] and Nakamura[60] were respectively, the camp doctor, interpreter, senior non-commissioned officer, and mess sergeant.

http://en.wikipedia.org/wiki/User:Jmcneill2

Reference 58 tells us
The charge and specifications against Asano were: Charge: That between 1 April, 1943 and 31 August, 1944, at Fukoka Prisoner of War Branch Camp Number 3, Kyushu, Japan, the accused Yukio Asana, then a civilian serving as an interpreter with the Armed Forces of Japan, a nation then at war with the United States of America and its Allies, did violate the Laws and Customs of War. Specification 1: That in or about July or August, 1943, the accused Yukio Asano, did willfully and unlawfully, brutally mistreat and torture Morris O. Killough, an American Prisoner of War, by beating and kicking him; by fastening him on a stretcher and pouring water up his nostrils. Specification 2: That on or about 15 May, 1944, at Fukoka Prisoner of War Branch Camp Number 3, Kyushu, Japan, the accused Yukio Asano, did, willfully and unlawfully, brutally mistreat and torture Thomas B. Armitage, William O Cash and Munroe Dave Woodall, American Prisoners of War by beating and kicking them, by forcing water into their mouths and noses; and by pressing lighted cigarettes against their bodies. Specification 5. That between 1 April, 1943 and 31 December, 1943, the accused Yukio Asano, did, willfully and unlawfully, brutally mistreat and torture John Henry Burton, an American Prisoner of War, by beating him; and by fastening him head downward on a stretcher and forcing water into his nose.

So he was charged with more than just the water torture.

BTW: Just so you know, US POWs have been subjected to mistreant of virtually every kind in virtually every war. IIRC many Vietnam POWs were accused of lying about it.